The present invention relates to improvements in take-off connectors for joining portions of circuits mounted on movable objects to portions of circuits which are stationary, and particularly to an improved take-off connector for use in electrical circuits in systems for monitoring physical security of buildings.
False alarms are one of the primary problems with electrically operated security systems. One common type of intrusion detection system for protecting windows uses an electrically conductive foil strip attached to the window as a part of a circuit which must remain intact to provide an indication of normal conditions. Whenever circuit continuity is broken, as when the window is broken, breaking the foil strip, the alarm controller senses an abnormal condition and provides an appropriate alarm. Loss of contact between the window-carried portion of such a circuit and the rest of the circuit, however, produces a false alarm.
To avoid false alarms it is necessary for such a circuit to use a take-off connector which reliably connects the movable window-carried portion of the circuit to the remainder of the circuit. Such a take-off connector should not develop an increasing resistance through its contact points, despite either frequent opening and closing of the window or long periods without being checked, and should properly connect the window-carried portion of the circuit to the stationary portion of the circuit without any special effort besides moving the window.
Because of the numerous different designs for the frames of movable windows it is desirable for the separate movable and stationary portions of such a take-off connector to be mountable for operation in more than one arrangement. It is also desirable for such a take-off connector to be operable by longitudinal sliding of the movable portion relative to the stationary position to permit alarm system actuation with a window in a permissible partly open position.
One type of previously known take-off connector includes small helical springs which urge pivotably mounted movable contact points toward fixed contact surfaces on the opposite portion of the take-off connector. Conductors are connected to the moving contact portion of such a connector at terminal posts connected to the helical springs. The electrical path extends through the helical springs and thence into the movable contact points. Circuit continuity in this type of take-off connector depends thus upon maintenance of good electrical contact between the spring and the contact point. There are, then, at least two locations in each electrical path through such a take-off connector where dirt or corrosion may build up to eventually interrupt the electrical path.
To reduce the possibility of such an interruption of the electrical circuit such take-off connectors commonly utilize a relatively high spring force (as much as five pounds for full depression of the movable contacts) to maintain an electrical path between the parts of the connector. This amount of force is unsuitable in an arrangement where one portion of the take-off connector slides along the other, because the force of the springs may be sufficient to lift the window frame from its proper position in its slide track, and because of the amount of contact surface wear likely to result. High spring force also makes adhesive mounting of such previously known connectors impractical.
Another known type of take-off connector utilizes a sheet metal flat spring as the movable contact. The movable contacts of such a connector each have an end shaped in a convex arc providing a line of contact against a flat fixed contact surface on the opposite portion of the take-off connector. The only commercially available take-off connectors of this type known to the applicants, however, utilize a significantly high spring force, making the unit at best marginally suitable for sliding, rather than directly approaching face to face contact. Additionally, these movable contacts have an exposed free end which is subject to being caught on one's clothing, causing the contact to bend out of alignment or to damage the clothing.
One known connector has a pair of narrow movable contact points of the resilient flat spring type mounted side by side, with the ends of the contacts protected. This arrangement of the contacts has the disadvantage that misalignment of the two portions of the connector, resulting, for instance, from a loose fit of a movable window, may result in an excessive number of false alarms.
What is needed, therefore, is an improved take-off connector for use in connecting a window-carried portion of a security circuit to a stationary portion of such a security circuit in connection with a wide variety of types of window frame arrangements, wherein the connector is usable in either a sliding or a face-to-face approach of the movable and stationary connector portions to one another, in which significant amount of misalignment is easily accommodated, and which operates reliably over long periods of time.